Microsystem with an element which can be deformed by a thermal sensor

ABSTRACT

The invention involves a microsystem which can be used in particular for making microswitches or microvalves, composed of a substrate ( 50 ) and used for shifting between a first state of functioning and a second state of functioning by means of a bimetal-effect thermal sensor. The sensor includes a deformable element ( 51 ) attached, at opposite ends, to the substrate ( 50 ) so that there is a natural deflection without stress with respect to a surface of the substrate opposite it, this natural deflection determining the first state of functioning, the second state of functioning being caused by the thermal sensor which, under the influence of temperature variation, induces a deformation of the deformable element ( 51 ) which diminishes the deflection by subjecting it to a compressive force which shifts it in a direction opposite to its natural deflection by buckling.

FIELD OF THE INVENTION

The present invention involves a microsystem with an element which canbe deformed by the action of a thermal sensor. Such microsystems can beapplied to microswitches for opening or closing electric circuits andmicrovalves for microfluid applications.

These microsystems include an element in the form of a beam or amembrane which is deformed by heat. Strongly non-linear behaviour issought in order to obtain a rapid shift between the two states, an openstate and a closed state.

It must be possible to design these microsystems so that they can becompatible with the making of microelectronic components.

STATE OF THE ART

The microsensors used to trigger the deformation of the deformableelement of a microsystem can be put in three main categories as afunction of the principles used. First, thermal sensors which usethermal dilatation of one or several of their components. There are alsoelectrostatic sensors which use the electrostatic force generatedbetween two elements with different charges. Lastly there are magneticsensors which use forces induced by a magnetic field.

There are also sensors which use piezoelectric and magnetostrictivematerials.

The thermal sensors appear to be the most useful because they generallyallow for larger deformations then electrostatic sensors whereasmagnetic sensors, or those which use piezoelectric and magnetostrictivematerials, are generally difficult to use with classic micro-machiningprocesses, particularly, for manufacturing which requires technologicalcompatibility with microelectronics. In addition, with a thermal sensor,it is easy to generalise the use of a controlled microswtich to athermal microswitch (change of state as of a critical temperature) or toa micro-circuit breaker (change of state as of a certain criticalcurrent intensity).

The simplest way to make a thermal sensor is to use a bimetal. Thistechnique involves two layers of materials having different thermaldilatation coefficients so that a variation in temperature of the wholeunit causes a deflection of the bimetal. Temperature elevation isobtained by the Joule effect either by directly passing an electricalcurrent into one of the two layers of the bimental or into the resistorsformed on one of these layers and obtained, for example, by implantationif one of the layers is made of silicon.

The deformation of the bimetal depends on the type of attachment to itssupport. FIG. 1 shows the deformation due to the effect of a thermalstress on a free bimetal, i.e. at the ends which are not attached butmerely supported, composed of a layer 1 and a layer 2 with differentthermal dilatation coefficients. The broken line shows the averageposition of the bimetal in the absence of a thermal stress. The theoryshows that in this case the radius of curvature □ is uniform. It isnegative if the coefficient of dilatation of layer 2 is greater thanthat of layer 1.

If the deformable structure is embedded at its ends, it is preferable,because of the appearance of the deformity, to place the bimetal in theareas where the dilatation effect acts in the direction of thecurvature. Depending on the location of the bimetal, an increase intemperature may deflect the structure in one direction or another.

FIG. 2 shows a first bimetal structure of this type. It includes a firstlayer 3 and a second layer 4 formed of two parts. The broken lineindicates the average position of the bimetal in the absence of athermal stress. As the thermal dilatation coefficient of the layer 4 isgreater than that of the layer 3, the deformation of the bimetalstructure due to the effect of dilatation is in the direction indicatedin FIG. 2.

FIG. 3 shows a second bimetal structure embedded at its ends. It has afirst layer 5, which is embedded, and a second layer 6 which is locatedon the central part of the layer 5. The broken line indicates theaverage position of the bimetal in the absence of a thermal stress. Asthe thermal dilatation coefficient of the layer 6 is greater than thatof the layer 5, the deformation of the bimetal structure due to theeffect of dilatation is in the direction indicated in FIG. 3.

The amplitude f of the deformation is proportional to the temperatureand the deformation thus depends on the surrounding temperature. It ispossible however to find structural configurations so that thedeformation is independent of the surrounding temperature.

Due to the complex mechanisms involved during the opening and closing ofan electric circuit however (electric arc, bounce phenomena, etc.), itis preferable to seek systems for which the change in state (the shiftfrom the open state of the circuit to its closed state) is as rapid aspossible. The ideal would be designing systems having a criticaltemperature beyond which the mechanical equilibrium state changes. Thiscannot be obtained with just a bimetal however.

The U.S. Pat. No. 5,463,233 discloses a micro-machined thermal switchwhich combines a bimetal and an electrostatic sensor. In the absence ofdeformation of the bimetal, the electrostatic force is weak, the bimetalis in equilibrium between the electrostatic force and the mechanicalrestoring force of the structure. When the temperature increases, thebimetal effect brings the electrodes of the sensor closer until theelectrostatic force becomes sufficiently strong to overcome themechanical restoring force and to thus trigger the instantaneous shiftof the structure.

Another way to generate a displacement by a change in temperature is toheat an embedded beam or membrane. FIG. 4 shows an embedded membrane 7in resting position along the broken line and the deformed position bythe solid line. The thermal dilatation compresses the structure. Thetheory of beams or membranes shows that there is a critical compressionstress (and thus a temperature) beyond which the structure buckles. Thearticle “Buckled Membranes for Microstructures” by D. S. Popescu et al.,which appeared in the IEEE review, pages 188-192 (1994), describes suchas structure in compression. In the case of a beam of thickness h,length L, made from a material with a dilatation coefficient α, thecritical compression stress is given by the equation: $\begin{matrix}{\theta_{cr} = \frac{\pi^{2}h^{2}}{3\alpha\quad L^{2}}} & (1)\end{matrix}$

The theory also shows that the amplitude f of the deformity of thestructure is given by the equation: $\begin{matrix}{f = {\pm \sqrt{\frac{\theta}{\theta_{cr}} - 1}}} & (2)\end{matrix}$

In the case of a square membrane, A is 2.298 h. One of the drawbacks ofthis method is the indeterminate nature of the sign of f. As FIG. 4shows, the membrane 7 may be deformed in the opposite direction and takethe position indicated by the broken line. Equation (2) also shows thatit is difficult to obtain high displacement amplitudes for structuresmade by surface technologies, i.e. in thin layers.

Another solution derived from the preceding one is to use a naturallybuckled membrane. This is obtained by using silicon oxide membranes forexample. The system thus has two stable positions${f = {{\pm A}\sqrt{\frac{S}{S_{cr}} - 1}}},$where S is the internal stress and S_(cr) is the critical bucklingstress. To shift from one position to another an additional mechanicalaction is needed. In the article mentioned above by D. S. Popescu etal., this additional mechanical action is from a field of pressure onthe membrane.

Embedded bimetals were studied in the article “Analysis of Mi-metalThermostats” by TIMOSHENKO which appeared in the Journal of the OpticalSociety of America, vol. 11, pages 233-255, 1925. This article gives inparticular a theoretical study of the structure shown in FIG. 5. Thedeformable structure is a beam 10 composed of a bimetal, the ends ofwhich are held by two fixed supports 11 and 12. The retention of theends eliminates the degree of freedom of translation but leaves thefreedom of rotation along an axis perpendicular to the plane of thefigure. At rest, i.e. at a temperature such that there is no thermalstress due to the bimetal effect, the beam, shown in solid lines in FIG.5, shows an initial deformation in a circle arc of radius □_(o). Whenthe temperature increases, the following effects are produced:

-   -   1st effect: the longitudinal thermal dilatation of the beam        being blocked by the supports 11 and 12, the beam is subjected        to a compression force.    -   2^(nd) effect: the bimetal is made so that an increase in        temperature causes an increase in the curvature. This produces a        downward deflection of the beam in FIG. 5,    -   3rd effect: due to the preceding effect, the length of the beam        decreases. This induces an additional internal compression        stress in the beam.

The first and third effects favour buckling of the structure, leading toshifting of the beam once a certain critical temperature is reached. Thebeam then takes the position indicated by the broken lines in FIG. 5.

The systems of the prior art; mentioned above show characteristics suchthat they cannot give a microsensor to deflect a membrane or a beamusing the thermal dilatation effects with the following advantages:

-   -   non-linearity between temperature and deflection to produce a        sudden change (shift and notion of critical temperature) with a        high amplitude;    -   no sensor other than that which produces the thermal dilatation        effect;    -   use of a thin-layer manufacturing technique, which requires        rigid embedding for the deformable element.

BRIEF DESCRIPTION OF THE INVENTION

To overcome the above-mentioned drawbacks, a microsystem is proposedwhich has its deformable element (beam or membrane) naturally deflectedat rest, this initial deflection not being of the buckling type. Thedeformable element is thus non-planar, as predefined by itsconstruction. This deformable element is embedded and the deformationcaused by the thermal sensor results from a bimetal effect and abuckling phenomenon induced by thermal dilatation. In the resting state,the embedding does not place any force on the deformable element.

The invention thus involves a microsystem on a substrate which is usedto produce a shift between a first state of functioning and a secondstate of functioning by means of a thermal sensor with a bimetal effect,the aforesaid sensor including a deformable element attached, by itsopposite ends, to the substrate so that it naturally has a deflectionwithout stress with respect to a surface of the substrate which isopposite it, this natural deflection determining the aforesaid firststate of functioning, the aforesaid second state of functioning beingtriggered by the aforesaid thermal sensor which induces, due to atemperature variation effect, a deformation of the deformable elementtending to diminish its deflection by subjecting it to a compressionstress which causes its shifting by a buckling effect in the directionopposite to that of its natural deflection. When the thermal controltriggered by the sensor is eliminated, the microsystem returns to itsfirst state of functioning.

The first state of functioning can correspond to a position of thedeformable element which is the furthest from the aforesaid surface ofthe substrate, the aforesaid second state of functioning correspondingto a position of the deformable element closest to the aforesaid surfaceof the substrate. The inverse situation is also possible.

The central part of the deformable element can be thicker than itsperipheral part.

The invention also involves a microswitch composed of a microsystem asdefined above, a system of electrodes being included in the microsystem,on the surface of the substrate and on the deformable element so thatthere is electrical continuity between electrodes in one of theaforesaid states of functioning and an absence of electrical continuityin the other of the aforesaid states of functioning.

The invention also involves a microvalve composed of a microsystem asdefined above, a fluid flow orifice being included in the microsystem sothat it is blocked in one of the aforesaid states of functioning andopen in the other of the aforesaid states of functioning.

The invention also involves a process for manufacturing a microsystem asdefined above, characterised in that:

-   -   the deformable element is obtained by depositing of an        appropriate layer of material on the aforesaid surface of the        substrate, this layer being attached to the aforesaid surface        with the exception of a part which forms an arch above the        aforesaid surface and which constitutes the deformable element,    -   means, obtained by depositing, are in close contact with the        aforesaid deformable element and constitute, along with it, the        aforesaid thermal sensor with bimetal effect.

The part forming the arch is advantageously obtained by a prior depositon the aforesaid surface of the substrate of a sacrificial mass to givea definite shape to the aforesaid deformable element once thesacrificial mass has been sacrificed, the sacrificial mass beingprovided so that, at the end of the process, the aforesaid deformableelement naturally has a deflection without stress with respect to theaforesaid surface of the substrate.

According to a first variant, the process includes the followingsuccessive steps:

-   -   depositing of a layer of sacrificial material on the aforesaid        surface of the substrate,    -   obtaining on the layer of sacrificial material a mass of        material which can flow without altering the substrate and the        sacrificial material,    -   flowing of the material which can flow to give at a shape which        is complementary to the desired arch shape of the deformable        element,    -   etching of the layer of sacrificial material and of the material        which has flowed until there remains on the aforesaid surface of        the substrate only the aforesaid sacrificial mass which        reproduces the shape of the material which flowed,    -   depositing of the layer which will provide the deformable        element,    -   depositing of the means to form, with the aforesaid deformable        element, the aforesaid thermal sensor,    -   elimination of the sacrificial mass.

In this case, the mass of material to flow can be obtained by depositingof a layer of photosensitive resin on the sacrificial material layer andby etching of this layer of photosensitive resin so that only the massof material which flows remains.

According to a second variant, the process includes the following steps:

-   -   obtaining on the aforesaid surface of the substrate a        sacrificial mass, with a step profile, and of a shape        essentially complementary to the shape of the arch desired for        the deformable element,    -   depositing of the layer to form the deformable element,    -   depositing of the means to form, with the aforesaid deformable        element, the aforesaid thermal sensor,    -   elimination of the sacrificial mass.

In this case, the sacrificial mass can be obtained by depositing on theaforesaid surface of the substrate of a layer of sacrificial materialand by successive etchings of this layer of sacrificial material untilthe surface of the substrate is reached with the exception of the placeof the deformable element where the etching lets the aforesaidsacrificial mass remain.

According to a third variant, the process includes the followingsuccessive steps:

-   -   obtaining on the aforesaid surface of the substrate a        sacrificial mass of uniform thickness at the place of the        deformable element,    -   depositing of the layer to provide the deformable element, the        deposit being done so that the part of this layer which covers        the mass of sacrificial material is naturally under stress,    -   depositing, on the previously deposited layer, of a layer in        which will be formed the means to form, with the aforesaid        deformable element, the aforesaid thermal sensor, this deposit        being done at a determined temperature so that, at the end of        the process, the deformable element is naturally deflected,    -   etching of the previously deposited layer to form the means,        with the aforesaid deformable element, for the aforesaid thermal        sensor,    -   elimination of the sacrificial mass.

In this case, the sacrificial mass can be obtained by depositing on theaforesaid surface of the substrate of a layer of sacrificial materialand by etching of this layer of sacrificial material.

Regardless of the process used, it may be necessary to include a stepinvolving opening the deformable element so that the opening of thisdeformable element allows for elimination of the sacrificial mass.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be better understood with the description whichfollows, given as a non-limiting example, accompanied by the appendeddrawings among which:

FIGS. 1 to 5, already described, represent devices with elements whichare deformable through the effect of a thermal sensor,

FIGS. 6A to 6H illustrate a first variant of a process for manufacturinga microsystem with an element which is deformable through the effect ofa thermal sensor according to the present invention,

FIGS. 7A to 7D illustrate a second variant of a process formanufacturing a microsystem with an element which is deformable throughthe effect of a thermal sensor according to the present invention,

FIGS. 8A to 8D illustrate a third variant of a process for manufacturinga microsystem with an element which is deformable through the effect ofa thermal sensor according to the present invention,

FIG. 9 is a cross section of a microswitch according to the presentinvention in the open state,

FIG. 10 is a cross section of a microswitch according to the presentinvention in the closed state,

FIG. 11 is a cross section of another microswitch according to thepresent invention in the open state,

FIG. 12 is a cross section of another microswitch according to thepresent invention in the closed state,

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

In general, structures obtained by microtechnology processes have planargeometry. Manufacturing of naturally deflected beams or membranes thusrequires particular attention.

The processes which will now be described deposit the deformable elementon a layer called the sacrificial layer which is then eliminated at theend of the process. A Si₃N₄ deformable element (beam or membrane) can bemade using a sacrificial layer of tungsten.

A first variant of the process according to the invention illustrated byFIGS. 6A to 6H yields a microsystem with a deformable element (beam ormembrane) which is non-planar and non-forced. On a substrate 20, made ofglass for example, the sacrificial layer 21 (made of tungsten forexample) is first deposited, then a layer of photosensitive resin 22(FIG. 6A). The resin layer is etched to leave only a mass of resin 23 ofwhich the area is determined by the desired deformable element (FIG.6B). By thermal treatment, the flow of the photosensitive resin istriggered. This yields a mass 24 with a shape complementary to that ofthe arch desired for the deformable element (FIG. 6C).

The sacrificial layer 21 is then etched. FIG. 6D shows a first step ofetching where the sacrificial layer 21 is etched on part of itsthickness at the places where this layer is not masked by the mass 24 ofresin. FIG. 6E shows a second etching step in which the mass 24 of resinhas been eliminated, by reactive ionic etching for example. Thesacrificial layer was simultaneously etched, reproducing the shape ofthe mass 24 in FIG. 6D. A mass 25 of sacrificial material is obtained.

The sacrificial mass as shown in FIG. 6E can be obtained directly byusing an organic material (a polyimide for example) as long as thismaterial can flow and withstand the steps in the manufacturing of thedeformable element without degradation.

The surface of the substrate 20 supporting the sacrificial mass 25 isthen covered with a layer 26, for example of Si₃N₄ or silicon, then alayer 27 of a conducting material such as aluminium, gold or nickel (seeFIG. 6F). The materials of layers 25 and 26 must have different thermaldilatation coefficients while being compatible with the later step offreeing the deformable element.

The layer 27 is then etched (see FIG. 6G) to demarcate the parts 28 ofthe thermal sensor.

The layer 26 is also etched. This etching is determined as a function ofthe shape which is desired for the deformable element (beam ormembrane). It also allows for opening the deformable element in order toallow for elimination of the sacrificial mass 25.

This yields the microsystem illustrated by FIG. 6H with a deformableelement 29 which is naturally deflected with respect to the surface ofthe substrate 20.

A second variant of the process according to the invention, illustratedby FIGS. 7A to 7D, yields a microsystem with a non-planar and non-forceddeformable element. A sacrificial layer 31 (see FIG. 7A) is deposited ona surface of a substrate 30. This sacrificial layer is etched severaltimes and with as many masks as needed to obtain a sacrificial mass 32,with a step profile, and in a shape which is essentially complementaryto the shape of the arch desired for the deformable element. Around thesacrificial mass 32, the surface of the substrate is apparent (see FIG.7B). As before, a layer 33 and a layer 34 to form the deformable elementand the thermal sensor are then deposited.

As before, the layer 34 is etched to obtain the parts 35. Likewise, thelayer 33 is etched as a function of the desired shape of the deformableelement and to open this deformable element in order to eliminate thesacrificial mass 32.

The microsystem illustrated by FIG. 7D with a deformable element 36which is naturally deflected with respect to the surface of thesubstrate 30 is obtained. The materials used can be the same as before.

A third variant of the process according to the invention, illustratedby FIGS. 8A to 8D, yields a microsystem with a planar and prestresseddeformable element in which the temperature difference will be adjustedduring the formation of the two parts of the bimetal.

A sacrificial layer is deposited on the surface of a substrate 40 and isthen etched to yield a mass 41 of uniform thickness at the place of thefuture deformable element (see FIG. 8A). Then a layer 42, made of SiO₂or Si₃N₄ for example, is deposited so that it covers the sacrificialmass 41 and the apparent surface of the substrate. This yields a part 43of the layer 42, which is rectilinear above the sacrificial mass 41 andnaturally stressed (see FIG. 8B). A second layer 44 is then deposited ata temperature greater than the surrounding temperature thus producing,at the end of the process, a natural deflection of the deformableelement.

As before, the layer 44 is etched to obtain parts 45 (see FIG. 8C).Likewise, the layer 42 is etched as a function of the desired shape ofthe deformable element and to open this deformable element in order toeliminate the sacrificial mass 41.

This yields the microsystem illustrated by FIG. 8D with a deformableelement 43 which is naturally deflected with respect to the surface ofthe substrate 40. The value of the prestress in the layer 42 must beadjusted to give buckling only when the bimetal structure is activated.

For example, the deformable element could be made of a beam of Si₃N₄ 1μm thick and 200 μm long. The initial deflection (at room temperature)of the beam can be 2 μm. The rest of the bimetal structure can be madeof aluminium and can be 1 μm thick. The structure shifts for atemperature variation between 100 and 120 C. The amplitude obtained ison the order of 5 μm while for a temperature variation from 0 to 100° C.the deflection is less than 1 μm.

The following figures illustrate examples of applications of theinvention which can be obtained with the processes described above.

FIG. 9 shows a microswitch formed on a substrate 50. The bimetal is madeof a deformable element 51, for example in the form of a beam, and oftwo parts 52. During the microsystem manufacturing process, electrodes53, 54 and 55 were included. Electrodes 53 and 54 were made before thedepositing of the sacrificial mass. Electrode 55 was made on thesacrificial mass, before the depositing of the bimetal layers.

It is also possible to design a microswitch which is normally closed asFIG. 10 demonstrates. The microswitch was formed on a substrate 60. Thebimetal is made of a deformable element 61 (beam or membrane) and a part62. Electrodes 63 and 64 were made before the depositing of thesacrificial mass. Electrode 65 was made on the sacrificial mass, beforethe depositing of the bimetal layers.

The normally closed state for the microswitch is obtained by using thethird variant of the process according to the invention and centeringthe part 62 on the deformable element 61.

It is clear that when the bimetal of FIGS. 9 and 10 shifts, there is apassage from the given functioning state to another functioning state.For FIG. 9, the shift of the bimetal allows for passage from the openstate (case shown in FIG. 9) to the closed state by the bringing intocontact of the electrode 55 with the electrodes 53 and 54. Themicrosystem of FIG. 10 functions inversely.

In order to provide a good electrical contact between the electrodeswhen the microswitch is closed, it is advantageous to make themodifications shown in FIG. 11. This figure represents a microswitchwhich is normally open, formed on a substrate 70 supporting theelectrodes 74 and 75. The deformable element 71 is formed by a thicklayer, locally thinned in order to rigidify the central part 72, whichis thus thicker, at the level of the electrode 73 borne by this centralpart. This also limits the influence of thermal dilatation induced bythe electrode 73.

Depending on the deposit thickness of the various layers, and accordingto the process used, it may also be advantageous to localise the areasof contact between the electrode 73 and the electrodes 74 and 75. Thiscan be obtained by a step of planarisation of the sacrificial layer or,as shown in FIG. 11, by making insets 76 obtained by photoetching of thesacrificial layer.

Another possible improvement involves using different materials to makethe other part of the bimetal, referenced as 80 on FIG. 11. The parts 80can include a first layer 81 adjacent to the deformable element and ofhigh resistivity (made of TiN for example), acting as a heating element.A second layer 82, superposed on the layer 81, having a high dilatationcoefficient, has a thermomechanical role. The layer 82 can be made ofaluminium. Depending on the materials used, it may be necessary toisolate the layers 81 and 82 by a fine layer of passivation 83.

FIG. 12 shows a cross section of a microvalve composed of a substrate 90pierced by a hole 91 which connects the two opposite sides of thesubstrate. The microvalve has a bimetal structure including a deformableelement 92 and one or several parts 93. The deformable element closes oropens the hole 91 as a function of the temperature induced in thebimetal.

1-10. (canceled).
 11. Process for manufacturing a microsystem assembledon a surface of a substrate (50, 60, 70, 90) which produces a shiftbetween a first state of functioning and a second state of functioningby means of a bimetal-effect thermal sensor, the aforesaid sensorincluding a deformable element (51, 61, 71, 92) attached, at oppositeends, to the surface of the substrate, the deformable element beingdeflected and concave in a first direction with respect to the surfaceof the substrate and being non-planar and non-stressed when in the firststate of functioning, and wherein temperature variation from a firsttemperature to a second temperature causes the sensor to shift into thesecond state of functioning while at the second temperature, said sensorshifting back into the first state of functioning when the temperaturevariation is no longer present, the temperature variation inducing thedeformable element (51, 61, 71, 92) to deflect in a direction oppositeto the first direction, the process comprising: depositing a layer (26,33, 42) of appropriate material on the aforesaid surface of thesubstrate (20, 30, 40) to obtain the deformable element (29, 35, 43),the layer being linked to the aforesaid surface with the exception of apart which forms an arch above the aforesaid surface and whichconstitutes the deformable element, and depositing means (28, 35, 45) onthe aforesaid deformable element (29, 35, 43).
 12. Process according toclaim 11, characterized in that the part which forms the arch isobtained by prior depositing, on the aforesaid surface of the substrate(20, 30, 40), of a sacrificial mass (25, 32, 41) to give a definiteshape to the aforesaid deformable element once the sacrificial mass (25,32, 41) being arranged so that, at the end of the process, the aforesaiddeformable element (29, 35, 43) has a natural deflection without stresswith respect to the aforesaid surface of the substrate (20, 30, 40). 13.Process according to claim 12, characterized in that it includes thefollowing successive steps: depositing of a layer of sacrificialmaterial (21) on the aforesaid surface of the substrate (20), obtainingon the layer of sacrificial material (21) a mass (23) of material whichcan flow without altering the substrate (20) and the sacrificialmaterial (21), flowing of the material which can flow to give it a shape(24) which is complementary to the desired arch shape of the deformableelement, etching of the layer of sacrificial material (21) and of thematerial which has flowed until there remains on the aforesaid surfaceof the substrate only the aforesaid sacrificial mass (25) whichreproduces the shape of the material which flowed, depositing of thelayer (26) which will provide the deformable element (29), depositing ofthe means (28) to form, with the aforesaid deformable element (29), theaforesaid thermal sensor, and eliminating the sacrificial mass (25). 14.Process according to claim 13, characterized in that the mass (23) ofmaterial to flow is obtained by depositing of a layer of photosensitiveresin (22) on the sacrificial material layer (21) and by etching of thislayer of photosensitive resin so that only the aforesaid mass (23) ofmaterial which flows remains.
 15. Process according to claim 12,characterized in that it includes the following successive steps:obtaining on the aforesaid surface of the substrate (30) a sacrificialmass (32), with a step profile, and of a shape essentially complementaryto the shape of the arch desired for the deformable element, depositingof the layer (33) to form the deformable element (36), depositing of themeans (35) to form, with the aforesaid deformable element (36), theaforesaid thermal sensor, and eliminating the sacrificial mass (32). 16.Process according to claim 12, characterized in that it includes thefollowing successive steps: obtaining on the aforesaid surface of thesubstrate (40) a mass (41) of sacrificial material of uniform thicknessat the place of the deformable element (43), depositing of the layer(42) to provide the deformable element, the deposit being done so thatthe part of this layer which covers the mass (41) of sacrificialmaterial is naturally under stress, depositing, on the previouslydeposited layer, of a layer (44) in which will be formed the means (45)to form, with the aforesaid deformable element (43), the aforesaidthermal sensor, this deposit being done at a determined temperature sothat, at the end of the process, the deformable element (43) isnaturally deflected, etching of the previously deposited layer to formthe means (45), with the aforesaid deformable element, for the aforesaidthermal sensor, and eliminating the sacrificial mass (41).
 17. Processaccording to claim 11, characterized in that there is a step involvingopening the deformable element (29, 36, 43) so that this opening of thedeformable element allows for elimination of the sacrificial mass (25,32, 41).